This invention relates in general to a tuning core apparatus and more particularly to such apparatus which, while enabling proper tuning positioning between the core and the coil, effectively minimizes the effect of vibrations on the core and coil during non-tuning periods which may otherwise give rise to undesirable microphonics in an associated radio in which the tuning core apparatus is incorporated.
It is known to tune radio receivers by axially sliding tuning cores or slugs relative to associated coils wound on tubular coil forms and to prevent relative axial movement when tuning adjustment is not desired. Some tuners also attempt to minimize relative radial (lateral) movement between the tuning core and coil. This has been accomplished in some prior tuners by firmly gripping (biasing) the tuning core against its associated tubular coil form, or support member, by members formed integral with the tubular coil form or support which contact and apply a pressure to the tuning core urging it against the internal surface of the tubular coil form or support. In other words, the coil form or support and core were constructed to provide a slidable friction press fit. This has not been altogether satisfactory from the standpoint that the friction loading forces acting on the tuning core in such tuners have resulted in requiring greater forces to provide the sliding axial operation necessary to accomplish tuning. Also, extremely close dimensional tolerances may be required in such friction fit prior tuners to prevent extremely high friction forces, and this adds to the expense of such prior tuners.
In the case of a pushbutton tuner in an automobile receiver, the mechanical driver forces necessary to overcome high friction forces acting on the tuning core can result in a malfunction to the pushbutton and/or the tuning operation. Further, with the advent of new and improved radio broadcast systems requiring very close tuning tolerances in the order of 250 cycles or less, the effect of vibrations on the tuning core may well give rise to undesirable microphonics in the receiver, and this means that the tuner must restrict all movement of the tuning core with respect to the coil to prevent detuning due to vibration. As a result there is a need for an inexpensive tuning apparatus which is easy to operate by pushbuttons but which minimizes the occurrence of microphonics in the associated receiver due to undesired relative axial and radial movement between the core and coil.